Effects of Body Mass and Age on the Pharmacokinetics of Subcutaneous or Hyaluronidase-facilitated Subcutaneous Immunoglobulin G in Primary Immunodeficiency Diseases

Population pharmacokinetics of immunoglobulin G after intravenous, subcutaneous, or hyaluronidase-facilitated subcutaneous administration in immunoglobulin-naive patients with primary immunodeficiencies

Immunoglobulin G (IgG) replacement therapy is the standard of care for patients with primary immunodeficiencies with antibody deficiencies. Intravenous (IVIG), subcutaneous (SCIG), and hyaluronidase-facilitated subcutaneous immunoglobulin (fSCIG) therapies differ in their pharmacokinetic (PK) profiles, administration routes, and dosing regimens. Information on use of subcutaneous therapy in IgG treatment-naive patients is limited. This study used population pharmacokinetic (popPK) model-based simulations to characterize IgG PKs in IgG-naive patients with varying disease severity across several IVIG, SCIG, and fSCIG dosing regimens. An integrated popPK model, developed and validated using data from eight clinical trials, was utilized to simulate scenarios that varied by therapy, loading regimen, maintenance dose (equivalent to 400, 600, or 800 mg/kg every 4 weeks [Q4W]), and baseline endogenous total IgG concentration (1.5 or 4.0 g/L). Simulations were performed for age groups of 2-<6, 6-<12, 12-<18, and ≥18 years. Steady-state serum trough IgG concentrations (Cmin,ss), proportion of patients achieving Cmin,ss ≥ 7 g/L, and days taken to reach this threshold were summarized. SCIG provided greater mean Cmin,ss values than IVIG and fSCIG for any scenario. Across all therapies, Cmin,ss tended to increase with age, dose, and endogenous concentration. Although the findings are model-based and not a summarization of real-world observations, doses ≥ 800 mg/kg Q4W with corresponding loading regimens are likely to be clinically appropriate for achieving target IgG concentrations in treatment-naive patients in a timely manner, especially at low endogenous starting concentrations. Therapy-specific dose adjustment based on baseline endogenous IgG concentration, clinical status, and patient characteristics may be warranted.